Production of high purity nickel-66

ABSTRACT

A METHOD HAS BEEN PROVIDED FOR THE PRODUCTION OF HIGH PURITY NICKEL-66 BY A DOUBLE NEUTRON CAPTURE RACTION WITH ENRICHED NI-64 IN A NEUTRON FLUX IN THE EXCESS OF ABOUT 2X10**15 N/CM.2$SEC. THE HIGH ENERGY (1.038 MEV.) GAMMA RADIATION FROM THE DAUGHTER CU-66 MAKES THE NI-66 A VERY USEFUL ISOTOPE IN NUMBEROUS TRACER DIFFUSION STUDIES AND RELATED INVESTIGATIONS, AS IN METALLURGICAL RESEARCH.

Mmdl 30 1971 J. J. PINAJIAN PRODUCTION OF HIGH PURITY NICKEL-G6.

Filed March 10, 1969 e i Q I .M 6 m D \Y noL lfl mmv r 7 M L I .h EDA 2 O LM I I p 75. WN AA U ZCE VM 6, 0 v r 6 w w m m INVENTOR. John J. Pinajian BY fl -44 ATTORNEY United States Patent 3,573,165 PRODUCTION OF HIGH PURITY NICKEL-66 John J. Pinajian, Oak Ridge, Tenn., assignor to the United States of America as represented by the United States Atomic Energy Commission Filed Mar. 10, 1969, Ser. No. 805,560 Int. Cl. G21g 1/02 U.S. Cl. 176-16 5 Claims ABSTRACT OF THE DISCLOSURE A method has been provided for the production of high purity nickel-66 by a double neutron capture reaction with enriched Ni-64 in a neutron flux in the excess of about 2 n/cmF-sec. The high energy (1.038 mev.) gamma radiation from the daughter Cu-66 makes the Ni-66 a very useful isotope in numerous tracer diffusion studies and related investigations, as in metallurgical research.

BACKGROUND OF THE INVENTION The present invention was made during the course of, or under, a contract with the U.S. Atomic Energy Commission.

This invention relates generally to methods for producing radioisotopes and more specifically to a method for producing high purity nickel-66.

In the art, the principal modes of producing 55-hr. Ni have been by high-energy proton-induced fission of uranium, tantalum, holmium, terbium, lanthanum, and silver; by high energy deuteron-induced fission of bismuth; and from the spallation of arsenic with high-energy deuterons. Both thermal and fast neutron-induced tertiary fissions of uranium have also yielded Ni. However, the yield of Ni in all of these methods is extremely small. The total fission cross section is generally small (a few barns at most) and the fission yield is only a fraction of this, resulting in a very small effective production cross section (microbarns to a few millibarns). In addition, the Ni must be separated from a large number of fission products, the overwhelming majority of Which are present in much greater concentrations than that of the Ni. Hence, considerable care and effort must be exercised to prepare a pure sample of Ni.

Radionickel is one of the tracer materials used in metallurgical studies. However, investigations involving the use of radioactive tracers of nickel have been severely handicapped by the absence of a radioactive isotope of nickel fulfilling anything but the minimum requirement necessary for its use. To be useful in tracer work in metallurgy, the nickel isotope should have a half-life sutficiently long to enable the investigator to complete the experiment with some margin for error. It should emit radiation which can be easily detected, but the detection should not require elaborate preparation and the interpretation of the data should require a minimum of correction factors. Due to the difiiculty in producing Ni in the past the choice of nickel isotopes has been between using isotopically enriched nickel requiring a mass spectrometer for the collection of data, or Ni which has a half-life of 92 years and emits a weak beta particle (E =0.067 mev.). The low energy of this emitted radiation necessitates careful and time-consuming processing steps for meaningful measurements. Furthermore, the long half-life gives rise to contamination problems in analysis area. Also long irradia tion times are required to produce useable quantities of Ni.

Of the other nickel isotopes, the long-lived Ni (T /2 80x10 years) is precluded from consideration not only because its half-life is too long, but because its use involves 3,573,165 Patented Mar. 30, 1971 X-ray counting. The 2.54-hr. Ni has too short a halflife to be of any but cursory value. There are, however, three radioisotopes of nickel which meet the requirements for use in metallurgy, namely: 6.4-day *Ni, 36-hr. "Ni, and SS-hr. Ni. The known methods for producing Ni give rise to low yields and the Ni has a half-life that is marginal. The Ni decays with a moderate energy beta particle (0.20 mev.) and, furthermore, the Cu daughter decays with a 1.039 mev. 'y-ray being emitted. This may be detected directly and thus simplifies any analysis. Accordingly, it can be seen that by providing an economical method of producing Ni many of the problems involved in using radioactive nickel in tracer studies will be eliminated.

SUMMARY OF THE INVENTION The method of this invention provides for economic production of practical amounts of Ni. Briefly, the method comprises the steps of enriching nickel in the isotope nickel-64, subjecting the enriched nickel-64 to a neutron flux of at least about 2.4 10 neutrons/cm. -sec. for a time sufiicient to convert the nickel-64 to the desired amount of nickel-66, separating the nickel-66 from impurities, and converting the separated nickel-66 into a form compatible with the intended use.

Accordingly, it is the primary object of the subject invention to provide an economical method for the production of practical amounts of Ni. This and other objects will become apparent upon a consideration of the following description of the preferred embodiment together with the drawing wherein the single figure shows a plot of calculated yield of Ni as a function of time and assumed cross sections along with experimental results.

DETAILED DESCRIPTION The subject development for economically producing Ni in useable quantities for tracer studies in metallurgy is accomplished by preparing a Ni target enriched greater than 98% in *Ni. The target is then irradiated in a thermal neutron flux of at least about 2 10 neutrons/cm. -sec. for the successive capture of neutrons by Ni. The target may be prepared in any conventional manner, as for example, by sealing *Ni metal powder in a conventional aluminum tube rabbit for insertion into a reactor to be irradiated.

After the target has been irradiated in a neutron flux the rabbit is allowed to cool before opening. The nickel is then dissolved in a solution of 15.7 M HNO with Ag carrier added in the form of AgNO to enhance the removal of silver impurities which are inherently present in the electromagnetically enriched *Ni due to sputter of the silver solder used on components of the separators Ag(n,'y) Ag]. The solution is then evaporated to incipient dryness. The residue is then taken up in water and made slightly alkaline with ammonium hydroxide; and AgCl is precipitated by adding hydrochloric acid. The AgCl is then removed by filtration. After filtration, H 50 is added to the filtrate, the solution is evaporated to strong fumes of S0 to remove the hydrochloric acid; then cooled and diluted with H O. This solution is neutralized with a basic solution and the nickel is then electroplated from the solution onto a platinum screen at approximately 2 amperes for a period suf'ficient to recover the nickel-66, using an ice bath and a magnetic stirrer. This effectively separates the Ni from the Na which is present. The Na is due to the normal sodium contamination of the nickel target plus that produced in the aluminum target container by the Al(n,a) Na reaction.

Upon removal of the Na, the Ni activity is removed from the screen by dissolution in hot 6 M HCl. The solution is made slightly acid by the addition of HCl and passed through a 100-200 mesh anion exchange column to remove the traces of cobalt present. The presence of cobalt-58 is brought about by the Ni(n,p) Co reaction and the minute amount of cobalt normally associated with materials that are enriched electromagnetically. The presence of this cobalt is probably a result of the electrical discharge occurring in stainless steel tanks of the electromagnetic separators in the enrichment process.

After the cobalt is removed, the eluate is evaporated down to incipient dryness, treated with HNO to destroy organic material, and then treated with HCl to convert the nickel to the chloride.

It has been found that the yield of Ni is in the order of three times that which would be expected. The calculated yields of Ni, Ni, and Ni and the experimental yields of Ni are shown in Table I.

Accordingly, a cross section for the second neutron capture reaction, Ni(n,'y) l li has been determined to be between 60 and 70 barns. The following example describes the subject process and the result in detail.

EXAMPLE Fifty mg. samples of *Ni metal powder having the isotopic analysis:

Mass: Atoms, percent 58 0.61 60 0.43 61 0.14 62 0.26 64 98.56

were irradiated in a neutron flux of 2.45 n./ cm. -sec. for periods of 48, 72 and 96 hrs., respectively. After a cooling period of 1.5 days, each aluminum hydraulic tube rabbit was opened and the nickel was dissolved in 15.7 M HNO Approximately 10 mg. of Ag carrier was added as AgNO and the solution was evaporated down to incipient dryness. The residue was taken up in water and made slightly alkaline with 14.8 M HN OH, and AgCl was precipiated with hydrachloric acid. The .AgCl was removed by filtration through a medium porosity sintered glass frit. Approximately 5 ml. of 36 M H 80 was added to the filtrate and the solution evaporated to strong fumes of sulfuric acid to remove the hydrochloric acid, then cooled, and diluted to 100 ml. with H O. This solution was neutralized with 14.8 M NH OH and an additional ml. of 14.8 M NH OH added. The nickel was electroplated from the solution onto a platinum screen, using an ice bath and a magnetic stirrer, at 2 amperes for a period of 1.5 hr. Ammonium hydroxide (25 ml. of 14.8 M) was added an dthe electroplating continued for an additional 0.5 hr. to ensure complete recovery of the Ni. This elfectively removed the Na contamination. The platinum screen was rinsed in dilute ammonium hydroxide and the Ni activity removed by dissolution in hot 7 M HCl. The solution was adjusted to 9 M in HCl and passed through a 100200 mesh, anion exchange column to remove cobalt. The eluate was evaporated down to incipient dryness, treated with 15.7 M HNO;, to destroy organic material, and then treated with 12 M HCl to convert the nickel to the chloride. The activity was then taken up in -15 ml. 0.1 M HCl.

Yields were determined by counting aliquots with a 3-in. x 3-in. Nal(Tl) gamma-ray spectrometer and were based on the 1.039 mev. transition (9%) in Zn populated from the decay of 5.1-min. Cu in equilibrium with the 55-hr. Ni. Approximately 20, 27, and 33 me. Ni

4 were available, as purified products, from the 48-, 72- and 96-hr. irradiations, respectively.

The figure shows the experimental yields as a function of irradiation time with a fiux 5) of 2.45 X 10 neutrons/ cmF-sec. as well as the calculated yields for the assumed cross sections (0' of 20, 50, 60, and barns. The cross section 0 for the Ni (11,7) Ni reaction was earlier determined to be 15:0.1 barns. Using the value of 1.5 barns, it can be seen that 0' is in the range of 60-70 barns instead of the originally expected 20 barns. This results in providing a yield of 3 times the expected yield.

As a result of the present method, essentially no chemical processing teps are required when the Ni is used in tracer studies such as diffusion studies. For such studies, samples of pure copper (99.999%), 0.360 in. diameter by 0.375 in. long, were electroplated on one end. The electroplating solution was prepared by admixing NiCl in hydrochloric acid, with inactive nickel sulfate, nickel chloride, and other standard ingredients, so that the composition was 20 g. NiSO 3.0 g. NiCl 10 g. NH Cl, and 10 g. H BO 1000 ml. H O. Plating was preformed for about 5 min. at 25 C. at a current density of 40-60 ma./Cm. The thickness of the resultant layer was about 0.5 micron. The plated samples were sealed in evacuated (5 10 torr) quartz capsules for heating. Diffusion anneal treatments were conducted at temperatures of 855 C., 903 C., 1005 C., and 1055 C. for periods of 172.45, 108.38, 76.42, 34, 60, and 70.50 hrs., respectively. One-mil sections were removed from each sample by standard lathesectioning techniques. The chips were collected in test tubes and 'y-counted directly without any treatment. Counting was accomplished with a conventional Nal(Tl) well-type crystal coupled to a single-channel pulse-height analyzer. This is in contrast to the required processing when Ni is used which has such a low energy fi-emission.

What is claimed is:

11. The method of producing the isotope nickel-66 comprising the steps of:

enriching nickel in the isotope nickel-64;

subjecting said nickel-64 to a neutron flux of at least about 2.4)(10 neutrons/cm. -sec.; and

separating said nickel-66 from impurities.

2. The method of claim 1 wherein said nickel-64 is enriched to a value of about 98 atoms percent.

3. The method of producing a gamma ray source for tracer analysis comprising the steps of:

enriching nickel in the isotope nickel-6 4;

irradiating said nickel-64 in a neutron flux of at least about 2.4)(10 neutrons/cmP-sec. for a time sufficient to convert said nickel-64 to the desired amount of nickel-66;

separating said nickel-66 from inherent impurities of isotopic silver, sodum and cobalt; and

converting said separated nickel-6 6 into a form suitable for tracer analysis use, said nickel-66 decaying to yield copper-66, a strong gamma-ray emitter.

4. The method of claim 3 wherein said nickel is irradiated in the form of a fine powder encased in an alurrunun'r container.

5. The method of claim 4 wherein the step of separating the nickel-66 from impurities includes the steps of 1) dissolving the nickel-66 in acid solution,

-(2) adding silver carrier to said solution,

(3) making said solution basic by adding ammonium hydroxide to the solution of step (2),

(4) precipitating silver impurities in the form of silver chloride by adding hydrochloric acid to the solution from step (3),

(5) removing the precipitate by filtration of the solution of step (4),

(6) adding sulfuric acid to the solution from step (4),

(7) evaporating the solution from step (6) to strong fumes of sulfuric acid to remove the hydrochloric acid,

(8) neutralizing the solution from step (7),

(9) electroplating the nickel-66 from the neutralized solution of step (8) onto a platinum screen for a period of time to ensure complete recovery of the nickel-66 thereby removing sodium-24 contamination,

(10) dissolving the nickel-66 from said platinum screen in hot hydrochloric acid, and

(11) passing the acid solution through an anion exchange column to extract the isotopic cobalt impurities for the solution of step (10).

References Cited UNITED STATES PATENTS 3,390,161 6/1968 Fraioli 176-14X 6 OTHER REFERENCES Nuclear Science Abstracts, vol. 16, August 1962, No.

LELAND A. SEBASTIAN, Primary Examiner 10 H. E. BEHREND, Assistant Examiner US. Cl. X.R. 23-312; 252-301.1 

